#include <iostream>
#include <algorithm>
using namespace std;
 
int main() {
    int N;
    cin >> N;
    
    bool exists[1001] = {false}; // 标记数字是否已存在 
    vector<int> uniqueNumbers;
    
    for (int i = 0; i < N; ++i) {
        int num;
        cin >> num;
        if (!exists[num]) {
            exists[num] = true;
            uniqueNumbers.push_back(num); 
        }
    }
    
    // 排序 
    sort(uniqueNumbers.begin(),  uniqueNumbers.end()); 
    
    // 输出结果 
    cout << uniqueNumbers.size()  << endl;
    for (int num : uniqueNumbers) {
        cout << num << endl;
    }
    
    return 0;
}
/**************************************************************
	Problem: 1183
	User: linmiaoling
	Language: C++
	Result: Compile Error
****************************************************************/